The use of powder diffraction in the study of molecular phase transitions

Abstract

An outline is given of the experimental techniques available for studying the structure of molecular systems through powder diffraction. A wide range of physical environments is possible with this technique making it appropriate for the study of phase transitions by means of structure. The difficulties encountered in the data analysis are enumerated and the limitations imposed by resolution are discussed. The state of the art is not yet fine enough for us to be able to put a high probability of success on neutron diffraction studies, though this is possible in practice. A new program to help in the search for unknown unit cells is described. The advantages of the fully operational program EDINP for the study of molecular phase transitions through the use of constrained refinements are stressed. A typical example of the type of system which can be studied in this way is presented, namely C₆D₆.C₆F₆, where the powder diffraction scans for the two phases are given for comparison.